Stem-changing verbs keep regular -AR, -ER or -IR endings but change their stem vowel in stressed syllables. Once you understand the boot verb pattern, the rule becomes predictable.
Practice free →Stem changes happen in the four forms where the stem is stressed: yo, tú, él/ella, ellos/ellas — the boot shape on a conjugation table. Nosotros and vosotros do NOT change because the stress falls on the ending.
The stressed e changes to ie: pensar (pienso, piensas, piensa, pensamos, pensáis, piensan). Other e→ie verbs: querer, empezar, sentir, preferir, entender, perder, venir (also irregular), tener (also irregular).
The stressed o changes to ue: poder (puedo, puedes, puede, podemos, podéis, pueden). Other o→ue verbs: volver, dormir, morir, encontrar, recordar, costar, jugar (u→ue).
Only -IR verbs: the stressed e changes to i: pedir (pido, pides, pide, pedimos, pedís, piden). Other e→i verbs: seguir, servir, repetir, vestirse, decir (also irregular).
When writing, if you are unsure whether a verb is stem-changing, use the nosotros form — it never changes and is always safe. Then build outwards.
Reading grammar explains the rules — but only active recall builds exam-ready memory. Practice typing these forms with instant feedback.
Start practicing free →Stem-changing verbs change their vowel in the stressed stem for four out of six persons: yo, tú, él/ella and ellos/ellas. Nosotros and vosotros do not change.
Common examples: pensar (e→ie), querer (e→ie), poder (o→ue), dormir (o→ue), pedir (e→i), seguir (e→i). The e→i pattern only occurs in -IR verbs.
Stem changes in the present tense follow the boot rule. In the preterite, only -IR verbs with o→ue or e→i changes affect the él and ellos forms (durmió, pidió). The future and conditional are not affected.
Written by Daniel Holmes for GCSE & A-Level Spanish students.